FRIDAY, June 10 (HealthDay News) — The chemical styrene, ubiquitous in foam coffee cups and take-out containers, has been added to the list of chemicals considered possible human carcinogens, according to a new U.S. government report.

On Friday, experts at the U.S. Department of Health and Human Services added styrene, along with five other chemicals — captafol, cobalt-tungsten carbide (in powder or hard metal form), certain inhalable glass wool fibers, o-nitrotoluene and riddelliine — to its list of 240 substances that are “reasonably anticipated” to be carcinogenic.

But before you toss those white plastic take-out containers, keep this in mind: the government report says that by far the greatest exposure to styrene comes from cigarette smoke. In fact, one study cited in the report estimates that exposure from smoking cigarettes was roughly 10 times that from all other sources, including indoor and outdoor air, drinking water, soil and food combined.

Styrene is a widely used chemical. Products that contain it include insulation, fiberglass, plastic pipes, automobile parts, drinking cups and other food containers and carpet backing, according to the Agency for Toxic Substances & Disease Registry.

Studies in the lab, animals and humans — particularly workers in industries such as reinforced plastic that expose them to higher than normal levels of the chemical — suggest that exposure to styrene causes damage in white blood cells, or lymphocytes and may raise the risk of lymphohematopoietic cancer, such as leukemia and lymphoma.

There is also evidence exposure may raise the risk of esophageal and pancreatic cancer among styrene-exposed workers, according to the Report on Carcinogens, prepared by the National Toxicology Program, part of the U.S. National Institutes of Health.

The report also issued its strongest warning about two other chemicals, formaldehyde (widely used as a preservative) and a botanical known as aristolochic acids, adding both to the list of “known” carcinogens.

“The strength of this report lies in the rigorous scientific review process,” said Ruth Lunn, director of the National Toxicology Program Office of the Report on Carcinogens, in a news release.

Aristolochic acids have been shown to cause high rates of bladder or upper urinary tract cancer in people with kidney or renal disease who consumed botanical products containing aristolochic acids, according to the report. Despite a U.S. Food and Drug Administration warning against the use of products containing aristolochic acids, it can still be purchased on the Internet and abroad, particularly in herbal products used to treat arthritis, gout and inflammation.

Formaldehyde has long been listed as a substance “reasonable anticipated” to cause cancer after animal studies showed it increased the risk of nasal cancer. Since then, additional studies in humans have shown exposure increases the risk for certain types of rare cancers, including nasopharyngeal (the nasopharnyx is the upper part of the throat behind the nose), sinonasal and myeloid leukemia, a cancer of the white blood cells, prompting federal officials to strengthen its warning.

Formaldehyde is a colorless, flammable, strong-smelling chemical that is widely used to make resins for household items, such as composite wood products, paper product coatings, plastics, synthetic fibers, and textile finishes. Formaldehyde is also used as a preservative in medical laboratories, mortuaries, and in some hair straightening products.

Representatives of industry took issue with the addition of both formadelhyde and styrene to the NTP’s list.

“It will unfairly scare workers, plant neighbors and could have a chilling effect on the development of new products,” Tom Dobbins, a spokesman for the American Composites Manufacturers Association, told The New York Times. “Our companies are primarily small businesses, and this could hurt jobs and local economies.”

The federal panelists were quick to stress that the public shouldn’t panic over the inclusion of any one substance in the Report on Carcinogens.

“A listing in the report does not by itself mean that a substance will cause cancer,” John Bucher, associate director of the NTP, told Bloomberg News in a conference call with reporters. Many factors, including the amount and duration of exposure, as well as an individual’s susceptibility can affect whether a person will develop cancer.